The present invention relates generally to machinery for manipulating electrodes and more particularly to devices and methods for joining graphite electrodes for use with metal arc furnaces.
Metal arc furnaces include large vessels for melting metal. Heat may be generated inside the furnaces using graphite electrodes across which electric current is passed. Heat is generated inside the furnace due to a high voltage arc formed by the current passing through one or more electrodes. The heat is used to melt metal.
During use, graphite electrodes are consumed within the furnace vessel, requiring electrodes to be replaced over time. As electrode material is consumed in the furnace, the electrode is shortened to a length where it is no longer independently usable. However, a partially-consumed electrode may be joined to a second partially-consumed or complete electrode to form a joined electrode that can be used. Thus, the partially-consumed electrode may still be useful when placed in combination with a second electrode portion.
Electrodes may be joined in an end-to-end configuration using a threaded joint in some applications. When electrodes are combined, electrical conductivity is generally maintained across the joint, and electricity may be passed from one electrode to the second in the joint electrode. A threaded joint is commonly used to join electrodes. The joining procedure requires at least one electrode to be rotated relative to a second electrode such that a threaded engagement occurs.
The joining process typically requires two stages. During a first stage, the first or free electrode is rotated relative to the second or fixed electrode to allow loose engagement of the corresponding threads. Rotation during this stage encounters relatively little resistance as the threads are rotating. This may be referred to as a spin-down rotation when a free electrode is spun about its longitudinal axis relative to a fixed electrode below the free electrode, to allow the threads to engage. In the second stage, or torque phase, an increase torque force is applied to the free electrode to tighten the free electrode to a manufacturer's suggested torque value.
Conventional tools and methods for joining electrodes in a threaded joint include powered electrode joining devices including an electrode holder that is configured to grip the fixed electrode, and a torque device that is configured to grip and spin the free electrode on the fixed electrode.
It is generally desirable to introduce the lower end of the free electrode into the electrode joining device at a specific distance above the upper end of the fixed electrode before the initial spin down occurs. The gap between the free electrode and the fixed electrode can help prevent damage to the threads on the electrodes as the free electrode is lowered down into the electrode joining device. Conventional techniques for setting the gap include manually placing a gap spacer on the upper end of the fixed electrode, lowering the free electrode until the free electrode meets the spacer, and then manually removing the spacer. Such a procedure is burdensome on workers and requires a worker to be near the joining zone, which can be unsafe.
What is needed then are improvements in electrode joint spacer apparatuses.